<?php

/**
 * Framework_Util_Uuid
 *
 *
 * @author Application Support Group
 * @copyright University of Georgia
 * @package BAMF
 * @filesource
*/


class Framework_Util_Uuid {

	/**
	* Generates a Universally Unique IDentifier, version 4.
	* 
	* RFC 4122 (http://www.ietf.org/rfc/rfc4122.txt) defines a special type of Globally
	* Unique IDentifiers (GUID), as well as several methods for producing them. One
	* such method, described in section 4.4, is based on truly random or pseudo-random
	* number generators, and is therefore implementable in a language like PHP.
	* 
	* We choose to produce pseudo-random numbers with the Mersenne Twister, and to always
	* limit single generated numbers to 16 bits (ie. the decimal value 65535). That is
	* because, even on 32-bit systems, PHP's RAND_MAX will often be the maximum *signed*
	* value, with only the equivalent of 31 significant bits. Producing two 16-bit random
	* numbers to make up a 32-bit one is less efficient, but guarantees that all 32 bits
	* are random.
	* 
	* The algorithm for version 4 UUIDs (ie. those based on random number generators)
	* states that all 128 bits separated into the various fields (32 bits, 16 bits, 16 bits,
	* 8 bits and 8 bits, 48 bits) should be random, except : (a) the version number should
	* be the last 4 bits in the 3rd field, and (b) bits 6 and 7 of the 4th field should
	* be 01. We try to conform to that definition as efficiently as possible, generating
	* smaller values where possible, and minimizing the number of base conversions.
	* 
	* @copyright Copyright (c) CFD Labs, 2006. This function may be used freely for
	*       any purpose ; it is distributed without any form of warranty whatsoever.
	* @author   David Holmes <dholmes@cfdsoftware.net>
	* @link http://www.php.net/manual/en/function.uniqid.php
	* @link http://www.ietf.org/rfc/rfc4122.txt
	* 
	* @return string A UUID, made up of 32 hex digits and 4 hyphens.
	*/
	
	function get() {
	 
	 // The field names refer to RFC 4122 section 4.1.2
	
	 return sprintf('%04x%04x-%04x-%03x4-%04x-%04x%04x%04x',
	   mt_rand(0, 65535), mt_rand(0, 65535), // 32 bits for "time_low"
	   mt_rand(0, 65535), // 16 bits for "time_mid"
	   mt_rand(0, 4095), // 12 bits before the 0100 of (version) 4 for "time_hi_and_version"
	   bindec(substr_replace(sprintf('%016b', mt_rand(0, 65535)), '01', 6, 2)),
	     // 8 bits, the last two of which (positions 6 and 7) are 01, for "clk_seq_hi_res"
	     // (hence, the 2nd hex digit after the 3rd hyphen can only be 1, 5, 9 or d)
	     // 8 bits for "clk_seq_low"
	   mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535) // 48 bits for "node" 
	 ); 
	}



}// end class


?>
